Gas turbine apparatus

ABSTRACT

A gas turbine apparatus is provided which comprises a turbine, a combustor for burning a mixture of air and fuel and providing the turbine with a combustion gas to drive it, a generator connected to the turbine to receive rotational force therefrom to generate electric power, a temperature sensor for measuring a temperature of an exhaust gas from the turbine, a temperature setting unit and a power setting unit. The power setting unit sets a set output power of the generator such that a first set output power is set when starting-up the generator, the first set output power is decreased at a first rate when the measured exhaust gas temperature reaches a second set temperature higher than a first target temperature, a currently set output power is decreased at a second rate higher than the first rate when the measured exhaust gas temperature reaches a third set temperature higher than the second set temperature after decreasing the set output power at the first rate, and a currently set output power is increased at a third rate smaller than the second rate when the exhaust gas temperature reaches a forth set temperature smaller than the first set temperature after

TECHNICAL FIELD

[0001] The present invention relates to a gas turbine apparatus, andmore particularly to a gas turbine apparatus in which an output power ofa generator can be adequately controlled based on a temperature of anexhaust gas of a gas turbine engine.

BACKGROUND ART

[0002] As a result of liberalization of the energy supply market, therehas been a significant growth in interest in the provision of localdistribution of energy. One means that is particularly suited to theprovision of a localized energy source is the gas turbine. Such aturbine generally comprises a generator that generates electric powerand a gas turbine engine for driving the generator. The turbine enginecomprises a turbine rotatably mounted on a rotation shaft, a combustorfor generating a combustion gas, a fuel control valve for controlling anamount of fuel supplied to the combustor, and an air compressor forcompressing air supplied to the combustor.

[0003] In the gas turbine apparatus described above, fuel an amount ofwhich is controlled by the fuel control valve and air which iscompressed by the air compressor, are supplied to the combustor to formtherein an air/fuel mixture. This air/fuel mixture is burnt by thecombustor to generate a combustion gas for supply to the turbine, tothereby rotate it at high speed. The generator is connected to one endof the rotation shaft and is driven by the turbine through the rotationshaft to generate electric power.

[0004] In the gas turbine apparatus as described above, a variety ofoperation controls such as a start-up control, a constant speedoperation control, and the like are performed by controlling an openingdegree of the fuel control valve. For example, generation of electricpower is controlled such that a detected temperature of an exhaust gasfrom the turbine is not allowed to exceed a predetermined value. Namely,a rise in output power from the generator is dependent on a rise in alevel of combustion in a combustor. As a consequence, a maximum outputpower of the generator is dependent on a maximum tolerance temperatureof an exhaust gas in the gas turbine engine.

[0005]FIG. 1 is a graph illustrating a relationship among an exhaust gastemperature EGT, a set power PWs and an actual output power PWa of thegenerator, according to a prior method for starting-up a generator. Whenpower is required to be supplied from the generator to a load, firstly agas turbine engine is, in general, started-up in a load-free state;under such a state, a turbine controller of a gas turbine apparatussets, at time t1, a set output power PWs of the generator at apredetermined value. Then, in response to the set output power PWs, anopening degree of a fuel control valve is gradually increased to therebyincrease an amount of fuel that is supplied, thereby causing an actualor process output power PWa from the generator to advance and an exhaustgas temperature (or process temperature) EGT to increase.

[0006] A gas turbine engine as described above is subject to an inherenttolerance maximum temperature Tmax of an exhaust gas temperature. A setoutput power PWs of the exhaust gas is determined so as to prevent aprocess or actual exhaust gas temperature EGT from the turbine reachingthe tolerance maximum temperature Tmax. In a case that the exhaust gastemperature EGT does reach the set temperature Ts at the time t2, asillustrated in FIG. 1, the set power PWs of the generator is decreasedat a predetermined rate. However, a case may occur wherein an actualoutput power PWa of the generator is significantly lower than a setoutput power PWs at time t2. In such a case, the actual output power PWsis controlled to further increase, with the result that the exhaust gastemperature EGT also further increases, resulting in a so-called“over-shooting” phenomenon, as shown in FIG. 1. When the set outputpower PWs of the generator is equal to the actual or process outputpower at time t3 as shown in FIG. 1, the actual output power PWs iscontrolled to be decreased in correspondence with the decreasing setoutput power PWs. Therefore, from time t3, the exhaust gas temperatureEGT is changed from a positive inclination to a negative inclination, asillustrated in FIG. 1. The exhaust gas temperature EGT graduallydecreases, and when it reaches the set temperature Ts at time t4, theset output power PWs of the generator is changed to increase at apredetermined rate. In response thereto, the exhaust gas temperature EGTbegins to increase again. In this way, the exhaust gas temperature EGTcan be substantially made to converge with the set temperature Ts,whereby the actual output power PWa can be made to substantiallyconverge with the power PWs.

[0007] In the prior art control method of a generator described above,the actual or process output power PWa of the generator is dependent onthe set temperature Ts of the exhaust gas, and the set temperature Ts ispredetermined by including a margin a for a tolerance maximumtemperature Tmax in view of any over-shooting phenomenon which occurs ata time of increasing the actual exhaust gas temperature. From this, itwill be apparent that in the prior control method a problem arises inthat an actual output power PWa is limited to a relatively low value asa consequence of a margin a of the exhaust gas temperature.

[0008] In some cases, in addition to the set temperature Ts, upper andlower set temperatures Tsu and Tsl are set, which are respectivelyhigher and lower than the set temperature Ts. The set output power PWsis decreased at a predetermined rate when the exhaust gas temperatureEGT becomes higher than a set upper temperature Tsu, while the power PWsis increased at a predetermined rate when the temperature EGT fallsbeneath that of the set lower temperature Tsl. From this description, itwill be apparent that an exhaust gas temperature EGT reaches a set upperset temperature Tsu at a time t2 in FIG. 1, thereby setting an outputpower PWs at a level lower than that of a predetermined rate, to therebyreduce a temperature EGT. In this context, it should also be pointedthat a temperature EGT reaches a set lower temperature Tsl at time t4,as shown in FIG. 1. As a result, the power PWs is increased at apredetermined rate to increase the temperature EGT. In this case, theexhaust gas temperature EGT can be substantially converged with the settemperature Ts, and thereby the actual output power PWa can besubstantially converged with the power PWs.

[0009] However, in the prior second control method using the upper andlower set temperatures, there exists a problem which may arise as aresult of increasing and decreasing rates in the set output power PWs.That is, if the changing rates are set to be relatively large, huntingphenomenon may occur at an actual output power PWa, resulting indestabilization of operation of an engine control system. On the otherhand, if the rates are set to be relatively low, it may take a long timeto convert the exhaust gas temperature EGT to the set temperature Ts,and “over-shooting” phenomenon may therefore readily occur.

[0010]FIG. 2 is a graph illustrating a relationship between an exhaustgas temperature EGT and a set output power PWs of a generator, in a casewhere increasing and decreasing rates of the set output power PWs arerelatively large. As is illustrated in FIG. 2, when the exhaust gastemperature EGT reaches an upper set temperature Tsu, the set outputpower PWs is lowered rapidly and hence the temperature EGT can bedecreased rapidly. Therefore, a problem of substantial over-shootingwherein the exhaust gas temperature EGT becomes much higher than theupper set temperature Tsu, is suppressed. However, rapid variation inthe set output power PWs produces hunting at an actual output power,which in turn produces hunting on the exhaust gas temperature EGT asshown in FIG. 2. As a result, operation of the control system isdestabilized.

[0011] Alternatively, an increase and decrease of the set output powerPWs may occur even after the exhaust gas temperature EGT reaches theupper and lower set temperatures Tsu and Tsl, respectively. The exhaustgas temperature EGT still increases gradually by thermal inertia whenthe temperature EGT exceeds the upper set temperature Tsu, because thedecreasing rate of the set output power PWs is small. Then, afterover-shooting, the temperature EGT decreases. However, the decreasingrate of the temperature EGT is slow due to the slow rate of decrease inthe set output power PWs. When the temperature EGT reaches the lower settemperature Tsl, the set output power PWs of the generator is increasedagain at a predetermined rate. Since the rate of increase is small, thetemperature EGT continues to decrease under thermal inertia, and afterover-shooting occurs it once again increases. As described above, underthe condition that the increasing and decreasing rates of the set outputpower PWs are small, over-shooting may occur. In addition, a long periodof time may be required to converge the temperature EGT and an actualoutput power.

DISCLOSURE OF THE INVENTION

[0012] It is therefore an object of the present invention to reduce“over-shooting” phenomenon of an exhaust gas temperature to therebyprovide stable operation of a gas turbine apparatus.

[0013] It is another object of the present invention to raise an actualoutput power of a generator in a gas turbine apparatus.

[0014] To achieve the above objects, a gas turbine apparatus accordingto a first aspect of the present invention comprises:

[0015] a turbine for providing rotational force;

[0016] a combustor for burning a mixture of air and fuel and providingsaid turbine with a combustion gas to drive it;

[0017] a generator connected to said turbine to receive the rotationalforce to generate electric power;

[0018] a temperature sensor for measuring a temperature of an exhaustgas from said turbine;

[0019] temperature setting means for setting a target temperature ofsaid exhaust gas as a first set temperature, a second set temperaturehigher than said first set temperature, a third set temperature higherthan said second temperature, and a fourth set temperature smaller thansaid first set temperature; and

[0020] power setting-means connected to said temperature sensor andtemperature setting means, for setting a set output power of saidgenerator as follows:

[0021] a first set output power is set when starting-up said generator;

[0022] said first set output power of said generator is decreased at afirst rate when said exhaust gas temperature measured by saidtemperature sensor reaches said second set temperature;

[0023] a currently set output power of said generator is decreased at asecond rate higher than said first rate when said exhaust gastemperature reaches said third set temperature after decreasing said setoutput power at said first rate; and

[0024] a currently set output power of said generator is increased at athird rate smaller than said second rate when said exhaust gastemperature reaches said forth set temperature after decreasing said setoutput power at said second rate.

[0025] In the gas turbine apparatus as above, it is preferable to set adifference between the first and second set temperatures to besubstantially equal to a difference between the first and fourth settemperatures. Further, it is preferable to set the first rate for use todecrease the set output power of the generator to be substantially equalto the third rate for use to increase the set output power of thegenerator.

[0026] Further more, it is preferable the temperature setting meansfurther comprises, set temperature increasing means for linearlyincreasing the exhaust gas set temperature from the first settemperature to a fifth set temperature near a tolerance maximum settemperature during a predetermined time period after the exhaust gastemperature measured by the temperature sensor converges on the firstset temperature, and then keeping the set temperature at the fifth settemperature. In such a case, it is preferable that the set temperatureincreasing means is adapted to set predetermined bands above and below afunction defining the linear increase of the exhaust gas set temperaturefrom the first set temperature to the fifth set temperature, and thepower setting means is adapted to decrease a currently set output powerat a predetermined rate when the exhaust gas temperature is higher thanthe upper band, and to increase a currently set output power at apredetermined rate when said exhaust gas temperature is lower than thelower band.

[0027] A gas turbine apparatus according to a second aspect of thepresent invention which comprises:

[0028] a turbine for providing rotational force;

[0029] a combustor for burning a mixture of air and fuel and providingsaid turbine with a combustion gas to drive it;

[0030] a generator connected to said turbine to receive the rotationalforce to generate electric power;

[0031] a temperature sensor for measuring a temperature of an exhaustgas from said turbine;

[0032] temperature setting means for setting a target temperature ofsaid exhaust gas as a first set temperature; and

[0033] power setting means connected to said temperature sensor andtemperature setting means, for setting a set output power of saidgenerator such that a first set output power is set when starting-upsaid generator, and said first set output power of said generator ischanged to a current process output power of said generator when saidexhaust gas temperature measured by said temperature sensor reaches saidfirst set temperature.

[0034] In this gas turbine apparatus, it is preferable that thetemperature setting means further comprises, set temperature increasingmeans for linearly increasing the exhaust gas set temperature from thefirst set temperature to a second set temperature near a tolerancemaximum set temperature during a predetermined time period after theexhaust gas temperature measured by the temperature sensor converges onthe first set temperature, and then keeping the set temperature at thesecond set temperature. In such a case, it is preferable that the settemperature increasing means is adapted to set predetermined bands aboveand below a function defining the linear increase of the exhaust gas settemperature from the first set temperature to the second settemperature, and the power setting means is adapted to decrease acurrently set output power at a predetermined rate when the exhaust gastemperature is higher than the upper band, and to increase a currentlyset output power at a predetermined rate when said exhaust gastemperature is lower than the lower band.

[0035] The present invention also provide a method for starting-up a gasturbine apparatus which comprises a turbine for providing rotationalforce, a combustor for burning a mixture of air and fuel and providingsaid turbine with a combustion gas to drive it, and a generatorconnected to said turbine to receive the rotational force to generateelectric power; said method comprising the steps of:

[0036] setting a set output power of said generator such that a firstset output power is set when starting-up said generator;

[0037] setting a target temperature of said exhaust gas as a first settemperature, a second set temperature higher than said first settemperature, a third set temperature higher than said secondtemperature, and a fourth set temperature smaller than said first settemperature;

[0038] decreasing said first set output power of said generator at afirst rate when said exhaust gas temperature measured by a temperaturesensor reaches said second set temperature;

[0039] decreasing a current set output power of said generator at asecond rate higher than said first rate when said exhaust gastemperature reaches said third set temperature after decreasing said setoutput power at said first rate; and

[0040] increasing a current set output power of said generator at athird rate smaller than said first rate when said exhaust gastemperature reaches said forth set temperature after decreasing said setoutput power at said second rate.

[0041] The present invention also provides another method for staring-upa gas turbine apparatus which comprises a turbine for providingrotational force, a combustor for burning a mixture of air and fuel andproviding said turbine with a combustion gas to drive it, and agenerator connected to said turbine to receive the rotational force togenerate electric power, said method comprising the steps of;

[0042] setting a set output power of said generator such that a firstset output power is set when starting-up said generator;

[0043] setting a target temperature of said exhaust gas as a first settemperature; and

[0044] changing said first set output power of said generator to acurrent process output power when said exhaust gas temperature measuredby said temperature sensor reaches said first set temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The advantage and principles of the present invention will beobvious to those skilled in the art of gas turbine apparatuses from thefollowing description of best modes for carrying out the invention withreference to the accompanying drawings. In the drawings,

[0046]FIG. 1 is a semantic graph showing a relationship between a setoutput power of a generator and an exhaust gas temperature in a priorgas turbine apparatus;

[0047]FIG. 2 is a semantic graph showing a relationship between a setoutput power of a generator and an exhaust gas temperature in a priorgas turbine apparatus in which the set output power is increased anddecreased at relatively higher rates;

[0048]FIG. 3A is a block diagram illustrating an embodiment of a gasturbine apparatus according to the present invention; and FIG. 3B is ablock diagram explaining a constitution of a turbine controller in thegas turbine apparatus illustrated in FIG. 3B;

[0049]FIG. 4 is a semantic graph illustrating a relationship between aset output power of a generator and an exhaust gas temperature,according to the present invention in a case where a first start-upcontrol process for the generator is executed in the gas turbineapparatus shown in FIGS. 3A and 3B;

[0050]FIG. 5 is a semantic graph illustrating a relationship between aset output power of a generator and an exhaust gas temperature,according to an assumed improvement of a prior art;

[0051]FIG. 6 is a semantic graph showing a relationship among set andactual output powers of the generator and an exhaust gas temperature,according to the present invention in a case where a second start-upcontrol process for the generator is executed in the gas turbineapparatus shown in FIGS. 3A and 3B;

[0052]FIG. 7 is a semantic graph showing a relationship among set andactual output powers of the generator and an exhaust gas temperature,according to the present invention, in a case where the second start-upcontrol process for the generator is executed and thereafter a settemperature value of an exhaust gas temperature is increased in the gasturbine apparatus shown in FIGS. 3A and 3B; and

[0053]FIG. 8 is a graphical diagram for explaining a case that the settemperature value has upper and lower bands, after time t3 in FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

[0054]FIG. 3 is a semantic block diagram illustrating a gas turbineapparatus according to a preferred embodiment of the present invention,and FIG. 3B is a block diagram illustrating a constitution of a turbinecontroller 13 incorporated in the gas turbine apparatus shown in FIG.3A. As illustrated in FIG. 3A, the gas turbine apparatus 100 accordingto the present invention comprises a turbine 1; a combustor 2 forburning an air/fuel mixture consisting of a fuel and air for generatinga combustion gas; a fuel control valve 14 for controlling an amount offuel supplied to the combustor 2; and an air compressor 3 for supplyingcompressed air to the combustor 2. The gas turbine apparatus 100 alsocomprises a heat exchanger 4 for heating air used for combustion by theheat of the combustion exhaust as; and the turbine controller 13 forcontrolling the turbine 1.

[0055] The gas turbine apparatus 100 is any one of micro gas turbineapparatuses and typical gas turbine apparatuses.

[0056] The turbine 1 has a plurality of rotor blades (not shown) whichreceive a fluid for rotation, and is rotatably supported on a rotationshaft 6 within a casing (not shown). The air compressor 3 is adapted tobe driven by the turbine 1 through the rotation shaft 6 in order tocompress air. The air compressor 3 is connected to the combustor 2through a pipe 7, such that air compressed by the air compressor 3 issupplied to the combustor 2 through the pipe 7. The heat exchanger 3 isinstalled midway along the pipe 7, so that the air compressed by the aircompressor 3 is heated by the heat exchanger 4 before it is supplied tothe combustor 2.

[0057] The fuel control valve 14 is disposed at an upstream side of thecombustor 2. A fuel supplied from a fuel supply source (not shown)passes through the fuel control valve 14 before it is supplied to thecombustor 2. An opening degree of the fuel control valve 14 is variable,so that the amount of fuel supplied to the combustor 2 can be adjustedby manipulating the opening degree.

[0058] The fuel and the air (through the pipe 7) supplied to thecombustor 2 form an air/fuel mixture within the combustor 2, and theair/fuel mixture is burnt within the combustor 2 to generate ahigh-temperature and high-pressure combustion gas. Then, this combustiongas is supplied to the turbine 1 to rotate it at high speed.

[0059] A generator 5 is connected to the end of the rotation shaft 6,and is rotated through the rotation shaft 6 by driving of the turbine togenerate electric power. The combustion gas supplied to the turbine 1 isexhausted after it is sent to the heat exchanger 4 through a pipe 8. Thealternating electric power generated by the generator 5 is adjusted foruse in commercial alternating electric power by an AC/DC converter, abooster, an inverter, etc., not shown, and thereafter is output. Actualoutput power is controllable to any value set by the inverter.Therefore, when an output power of the generator is set by the turbinecontroller 13, the generator 5 can supply a load with any level ofoutput power within a level of energy output from the turbine 1.

[0060] The gas turbine apparatus 100 comprises a variety of sensors. Theturbine controller 13 controls the opening degree of the fuel controlvalve 14, the set output power of the generator and so on, based onvalues measured by the sensors. The sensors include a rotational speedsensor 12 which measures a current rotational speed (or the number ofrotations per unit time period) NR of the rotation shaft 6. In aconstant-speed drive mode, the opening degree of the fuel control valve14 is feedback-controlled so as to maintain the rotational speedconstant. A temperature sensor (EGT sensor) 16 for measuring atemperature EGT of an exhaust gas from the turbine 1, is provided at acombustion gas exhauster thereof. The output power of the generator iscontrolled so that the exhaust gas temperature never exceeds a tolerancemaximum temperature.

[0061] As shown in FIG. 3B, the turbine controller 13 of the gas turbineapparatus 100 shown in FIG. 3A, comprises a temperature setting unit 131for setting a temperature Ts of the combustion exhaust gas from theturbine 1, a power setting unit 132 for setting an output power PWs ofthe generator 5 in response to the set temperature Ts and a measuredcurrent temperature EGT from the temperature sensor 16, and a valveoperating unit 133 for controlling the opening degree of the fuelcontrol valve 14 in response to the set output power PWs. It is to benoted that FIG. 3B illustrates only the units 131-133 which arenecessary to start-up the generator 5 according to the presentinvention, and does not illustrate other elements or units for othercontrols in the gas turbine apparatus 100.

[0062] A generator control operation by the turbine controller 13according to the present invention will next be explained with referenceto FIGS. 4-8.

[0063]FIG. 4 is a semantic graph showing a relationship between a setoutput power PWs and a measured exhaust gas temperature EGT from thetemperature sensor 16, in a case where a first generator start-upcontrol process according to the present invention is performed. FIG. 5is also a semantic graph showing a relationship between a set outputpower PWs and a measured exhaust gas temperature EGT, in an assumedprocess which is an improvement of the prior arts explained above withreference to FIGS. 1 and 2. In each of FIGS. 4 and 5, the set outputpower PWs of a generator is indicated by a dotted line, while theexhaust gas temperature EGT is indicated by a solid line. Such agenerator start-up control process made on the basis of the set outputpower PWs and the set temperature Ts of the exhaust gas is carried outwhile increasing an actual output power of the generator from zero to arated output power, after starting-up the gas turbine apparatus 100 andcontrolling the rotational speed NR of the turbine 1 at a predeterminedlevel. As described above, since an actual output power PWa of thegenerator corresponds to a combustion level in the gas turbine engine,the temperature EGT of the exhaust gas increases in response to theadvance of the actual output power PWa of the generator.

[0064] Before explaining the first generator start-up control processaccording to the present invention, the control process relating to FIG.5 will be explained. As mentioned above, this process has been assumedas an improvement of the prior arts explained with reference to FIGS. 1and 2. As illustrated in FIG. 5, the improved process employs two setupper temperatures which are above a target set temperature Ts and twolower set temperatures which are below the target temperature Ts.Namely, in the process, an outer upper set temperature Tsuo and an innerupper set temperature Tsui (Tsuo>Tsui) are utilized instead of the upperset temperature Tsu shown in FIG. 2, while an outer lower settemperature Tslo and an inner lower set temperature Tsli (Tslo<Tsli) areutilized instead of the lower set temperature Tsl shown in FIG. 2. Whenthe exhaust gas temperature (or measured temperature) EGT exceeds theinner upper set temperature Tsui at time t1, the set output power PWs iscontrolled to decrease at a lower rate. When the temperature furtherexceeds the outer upper set temperature Tsuo at time t2, the set outputpower PWs is controlled to decrease at a higher rate. Similarly, whenthe temperature EGT falls below the inner lower set temperature Tsli attime t3, the set output power PWs is controlled to increase at a lowerrate, and when the temperature EGT further falls below the outer lowerset temperature Tslo at time t4, the set output power PWs is controlledto increase at a higher rate.

[0065] By setting the two temperature levels (or inner and outer settemperatures) instead of each of the upper and lower set temperaturesTsu and Tsl, it becomes possible to vary the set output power PWs of thegenerator at both the lower and higher rate. Specially, since the setoutput power PWs is controlled to decrease rapidly when the temperatureEGT exceeds the outer upper set temperature Tsuo, “over-shooting”phenomenon wherein the actual exhaust gas temperature EGT risesexcessively above the temperature Tsuo may be suppressed. Moreover,since the set output power PWs is controlled to increase or decrease atthe lower rate when the temperature EGT becomes lower or higher than theinner lower or upper set temperature Tsli or Tsui, the generatorstart-up control operation is made more stable.

[0066] However, even if the outer and inner upper set temperatures andouter and inner lower set temperatures are employed at both upper andlower sides of the target set temperature Ts, a problem occurs that theset output power PWs of the generator swings significantly, and hencethe temperature EGT also swings significantly, as shown in FIG. 5.

[0067] In view of the above problems of the assumed improved process,the inventors of the present invention have further improved the processto thereby accomplish the first generator start-up control process. Inthe first control process, a predetermined target set temperature Ts ofthe generator, outer and inner upper set temperatures Tsuo and Tsuiwhich are higher than the set temperature Ts and an inner lower settemperature Tsli which is lower than the set temperature Ts asillustrated in FIG. 4 are provided and stored at the temperature settingunit 131 of the turbine controller 13 (FIG. 3B). An outer lower settemperature Tslo as shown in FIG. 5 is not set or stored in thetemperature setting unit 131. The power setting unit 132 monitors andcompares the exhaust gas temperature EGT from the temperature sensor 16with the set temperatures Tsuo, Tsui, and Tsli, and changes the setoutput power PWs to decrease at a predetermined lower rate when thetemperature EGT exceeds the set temperature Tsui at time t1, and thendecreases at a predetermined higher rate when the temperature EGTexceeds the set temperature Tsuo at time t2. Thereafter, when thetemperature EGT falls to the set temperature Tsli at time t3, the powersetting unit 132 changes the set output power PWs to increase at apredetermined lower rate.

[0068] It is preferable to set a difference between the set temperaturesTsui and Ts to be substantially equal to that between the settemperatures Tsli and Ts. Further, it is preferable to set them suchthat the predetermined decreasing rate when the temperature EGT exceedsthe set temperature Tsui is substantially equal to the predeterminedincreasing rate when the temperature EGT falls below the temperatureTsli.

[0069] As explained above, in the turbine control unit 13, the fourtemperatures Tsuo, Tsui, Ts and Tsli are previously set and stored inthe temperature setting unit 131, and the set output power PWs arechanged as shown in FIG. 4 by the power setting unit 132 in accordancewith the temperature EGT from the sensor 16; and the opening degree ofthe: fuel control valve 14 is adjusted by the valve operating unit 133in response to the set temperature PWs. In other words, the turbinecontroller 13 sets the output power PWs of the generator equal to apredetermined value such as a rated value, as shown in FIG. 4, at thetime of generator start-up, and thereby the opening degree of the fuelcontrol valve 14 is gradually opened to increase an amount of fuelsupplied. By increasing the amount of fuel supplied, an actual (orprocess) power outputted from the generator increases, for example, fromzero towards the rated output power. As the actual output powerincreases, the exhaust gas temperature EGT increases. When thetemperature EGT exceeds the inner upper set temperature Tsui (at timet1), the set output power PWs of the generator is changed to decreaseslowly and hence the actual output power thereof is also controlled todecrease slowly. However, the temperature EGT continues to increase dueto thermal inertia, and, thereafter, when the temperature EGT reachesthe outer upper set temperature Tsuo (at time t2), the set output powerPWs of the generator is changed to decrease rapidly. Therefore,“over-shooting” phenomenon of the temperature EGT is suppressed, and thetemperature EGT falls rapidly. When the temperature EGT falls to orbelow the inner lower set temperature Tsli (at time t3), the set outputpower PWs of the generator is switched to increase slowly.

[0070] Since an outer lower set temperature Tslo and hence a rapidincreasing rate are not employed in the first control process of thepresent invention, the exhaust gas temperature EGT can graduallyconverge in a range between the set temperatures Tsui and Tsli andhaving a center at the target set temperature Ts. Therefore, a problemsuch that the actual exhaust gas temperature EGT and the actual outputpower PWs of the generator swing, is avoided, and thus a stablegenerator start-up operation can be accomplished.

[0071] According to the first generator start-up control process, theexhaust gas temperature EGT can be controlled up to around the outerupper set temperature Tsuo, without any substantial “over-shooting”phenomenon. Therefore, the target temperature or set temperature Ts canbe set to be near the tolerance maximum temperature Tmax which is theso-called tripping exhaust gas temperature. The tripping exhaust gastemperature is referred to a set temperature for safety to trip theapparatus so as to stop a supply of energy from the generator when anexhaust gas temperature reaches it. Therefore, in the gas turbineapparatus 100 according to the present invention, the generator cansubstantially provide a tolerance maximum output power. Moreover, since“over-shooting” phenomenon of the temperature EGT is suppressed, a rateof increase in the output power of the generator can be set to berelatively large. As a result, the gas turbine apparatus 100 is capableof starting-up within a short time period.

[0072]FIG. 6 is a semantic graph for use in explaining a secondgenerator start-up control process according to the present invention,executed in the gas turbine apparatus 100 shown in FIGS. 3A and 3B. InFIG. 6, EGT plots a temperature of a combustion exhaust gas measured bythe temperature sensor 16, PWs plots a set output power which isvariably set at the power setting unit 132, and PWa plots an actualoutput power from the generator 5. Ts denotes a target set temperaturewhich is set at the temperature setting unit 131.

[0073] In the second start-up control process, a set output power PWs isset at a predetermined value at time t1 in the power setting unit 132.In the gas turbine apparatus 100, an opening degree of the fuel controlvalve 14 gradually becomes higher under control of the valve operatingunit 133, to thereby increase the actual output power PWa toward the setoutput power PWs. As the actual output power PWa increases, the exhaustgas temperature EGT also increases, and reaches the target settemperature Ts at time t2.

[0074] When the temperature EGT exceeds the temperature Ts at time t2,the power setting unit 132 changes the set output power PWs to theactual output power PWa. Since the set output power PWs is switched tobe equal to the actual output power PWa, the opening degree of the fuelcontrol valve 14 is held at that time. Accordingly, since the openingdegree of the fuel control valve 14 is not changed at time t2 and isheld constant thereafter, “over-shooting” of the exhaust gas temperatureEGT which occurs from time t2 can be greatly suppressed. FIG. 6illustrates, for purposes of comparison with the control process of thepresent invention, a dotted line denoting an exhaust gas temperatureinvolving significant over-shooting phenomenon, which may occur in theprior art.

[0075] By employing the second start-up control process of the presentinvention, the target temperature Ts of the exhaust gas can be set to ahigher value Ts near the tolerance maximum temperature Tmax. By settingthe target temperature Ts to be relatively high, the set output powerPWs and thus the actual output power PWa can be raised.

[0076] After the exhaust gas temperature EGT substantially convergeswith the target temperature Ts following either of the first or secondgenerator start-up control process, a generator power up-shiftingprocess is performed in the gas turbine apparatus 100. The powerup-shifting process will next be explained with reference to FIGS. 7 and8. FIG. 7 is the graph of FIG. 6 to which variations in the temperatureEGT, the set output power PWs and the actual output power PWa from timet3 have been added. It is to be noted here that although the followingdescription relates to a power shifting process following the secondstart-up control process as explained above with reference to FIG. 6,the power shifting process follows the first start-up control process,as explained above with reference to FIG. 4.

[0077] After performing the second start-up control process to convergethe temperature EGT with the target temperature Ts during time periodt1-t3, the output power up-shifting control process is performed fromtime t3.

[0078] In the output power shifting control process, the target settemperature Ts is gradually increased at the temperature setting unit131, as shown in FIG. 7. The temperature setting unit 131 stores threesubstantially linear functions indicative of variations in the targettemperature Ts, an upper set temperature Tsu higher than the temperatureTs and a lower set temperature Tsl smaller than the temperature Ts, asillustrated in FIG. 8. The upper and lower set temperatures Tsu and Tslare referred to as reference temperatures for switching the set outputpower PWs down and up, respectively.

[0079] After time t3, the set temperatures Ts, Tsu and Tsl are graduallyincreased in the temperature setting unit 131, and thereby the actualtemperature EGT falls below the lower set temperature Tsl. Such acondition is monitored and detected at the power setting unit 132, whichupon detection, increases the set output power PWs to thereby cause thevalve operating unit 133 to increase the opening degree of the fuelcontrol valve 14. Accordingly, the actual output power PWa and thetemperature EGT become higher. During the rise in the temperature EGTcaused by increasing the set output power PWs, if the EGT reaches theupper set temperature Tsu, the set output power PWs is controlled todecrease it. In such a manner as described above, the actual outputpower PWa is gradually increased, following the increase in settemperature Ts. An increasing rate (or a gradient of the function of Tsin FIG. 8) is sufficiently shallow for the actual temperature EGT andactual output power PWa of the generator to substantially follow theincrease without any substantial vibration being generated.

[0080] Finally, when the set temperature Ts reaches a certaintemperature close to the tolerance maximum temperature Tmax, the setoutput power PWs is not increased and fixed at the temperature.Therefore, after time t4, the gas turbine apparatus 100 can operate in acondition that the temperature EGT is nearly equal to the tolerancemaximum temperature Tmax, and thus can provide an actual output powersubstantially equal to a maximum available output power of thegenerator.

[0081] Although in the example described, the upper and lower settemperatures Tsu and Tsl, as well as the set centered temperature Ts,are employed in the power shifting control process, outer and innerupper set temperatures may be used instead of the single upper settemperature; and outer and inner lower set temperatures may be usedinstead of the lower set temperature. In such a case, as has beenexplained with reference to FIG. 4, increases and decreases in rates ofthe set output power PWs after the EGT reaches the outer lower and upperset temperatures, are greater than those after the EGT reaches the innerupper and lower set temperatures. By employing the four settemperatures, outer and inner, upper and lower set temperatures, the EGTcan rapidly converge with the increasing set temperature Ts.

[0082] It is to be understood from the foregoing that a gas turbineapparatus according to the present invention is not limited to theexamples described above, and may be modified in various ways withoutdeparting from the spirit of the invention.

1. A gas turbine apparatus comprising: a turbine for providingrotational force; a combustor for burning a mixture of air and fuel andproviding said turbine with a combustion gas to drive it; a generatorconnected to said turbine to receive the rotational force to generateelectric power; a temperature sensor for measuring a temperature of anexhaust gas from said turbine; temperature setting means for setting atarget temperature of said exhaust gas as a first set temperature, asecond set temperature higher than said first set temperature, a thirdset temperature higher than said second temperature, and a fourth settemperature smaller than said first set temperature; and power settingmeans connected to said temperature sensor and temperature settingmeans, for setting a set output power of said generator as follows: afirst set output power is set when starting-up said-generator; saidfirst set output power of said generator is decreased at a first ratewhen said exhaust gas temperature measured by said temperature sensorreaches said second set temperature; a currently set output power ofsaid generator is decreased at a second rate higher than said first ratewhen said exhaust gas temperature reaches said third set temperatureafter decreasing said set output power at said first rate; and acurrently set output power of said generator is increased at a thirdrate smaller than said second rate when said exhaust gas temperaturereaches said forth set temperature after decreasing said set outputpower at said second rate.
 2. A gas turbine apparatus according to claim1, wherein a difference between said first and second set temperaturesis set to be substantially equal to a difference between said first andfourth set temperatures.
 3. A gas turbine apparatus according to claim1, wherein said first rate for use to decrease the set output power ofsaid generator is set to be substantially equal to said third rate foruse to increase the set output power of said generator.
 4. A gas turbineapparatus according to claim 1, further comprising: means for setting anopening degree of a valve for providing said fuel to said combustor, inresponse to a set output power currently set in said power settingmeans.
 5. A gas turbine apparatus according to claim 1, wherein saidtemperature setting means further comprises: set temperature increasingmeans for linearly increasing said exhaust gas set temperature from saidfirst set temperature to a fifth set temperature near a tolerancemaximum set temperature during a predetermined time period after saidexhaust gas temperature measured by said temperature sensor converges onsaid first set temperature, and then keeping said set temperature atsaid fifth setting temperature.
 6. A gas turbine apparatus according toclaim 5, wherein said set temperature increasing means is adapted to setpredetermined bands above and below a function defining the linearincrease of said exhaust gas set temperature from said first settemperature to said fifth set temperature, and said power setting meansis adapted to decrease a currently set output power at a predeterminedrate when said exhaust gas temperature is higher than the upper band,and to increase a currently set output power at a predetermined ratewhen said exhaust gas temperature is lower than the lower band.
 7. A gasturbine apparatus comprising: a turbine for providing rotational force;a combustor for burning a mixture of air and fuel and providing saidturbine with a combustion gas to drive it; a generator connected to saidturbine to receive the rotational force to generate electric power; atemperature sensor for measuring a temperature of an exhaust gas fromsaid turbine; temperature setting means for setting a target temperatureof said exhaust gas as a first set temperature; and power setting meansconnected to said temperature sensor and temperature setting means, forsetting a set output power of said generator such that a first setoutput power is set when starting-up said generator, and said first setoutput power of said generator is changed to a current process outputpower of said generator when said exhaust gas temperature measured bysaid temperature sensor reaches said first set temperature.
 8. A gasturbine apparatus according to claim 7, further comprising: means forsetting an opening degree of a valve for providing said fuel to saidcombustor, in response to a set output power currently set in said powersetting means.
 9. A gas turbine apparatus according to claim 7, whereinsaid temperature setting means further comprises: set temperatureincreasing means for linearly increasing said exhaust gas settemperature from said first set temperature to a second set temperaturenear a tolerance maximum set temperature during a predetermined timeperiod after said exhaust gas temperature measured by said temperaturesensor converges on said first set temperature, and then keeping saidset temperature at said second set temperature.
 10. A gas turbineapparatus according to claim 9, wherein said set temperature increasingmeans is adapted to set predetermined bands above and below a functiondefining the linear increase of said exhaust gas set temperature fromsaid first set temperature to said fifth set temperature, and said powersetting means is adapted to decrease a currently set output power at apredetermined rate when said exhaust gas temperature is higher than theupper band, and to increase a currently set output power at apredetermined rate when said exhaust gas temperature is lower than thelower band.
 11. A method for starting-up a gas turbine apparatus whichcomprises a turbine for providing rotational force, a combustor forburning a mixture of air and fuel and providing said turbine with acombustion gas to drive it, and a generator connected to said turbine toreceive the rotational force to generate electric power; said methodcomprising the steps of: setting a set output power of said generatorsuch that a first set output power is set when starting-up saidgenerator; setting a target temperature of said exhaust gas as a firstset temperature, a second set temperature higher than said first settemperature, a third set temperature higher than said secondtemperature, and a fourth set temperature smaller than said first settemperature; decreasing said first set output power of said generator ata first rate when said exhaust gas temperature measured by a temperaturesensor reaches said second set temperature; decreasing a current setoutput power of said generator at a second rate higher than said firstrate when said exhaust gas temperature reaches said third settemperature after decreasing said set output power at said first rate;and increasing a current set output power of said generator at a thirdrate smaller than said second rate when said exhaust gas temperaturereaches said forth set temperature after decreasing said set outputpower at said second rate.
 12. A method for staring-up a gas turbineapparatus which comprises a turbine for providing rotational force, acombustor for burning a mixture of air and fuel and providing saidturbine with a combustion gas to drive it, and a generator connected tosaid turbine to receive the rotational force to generate electric power,said method comprising the steps of; setting a set output power of saidgenerator such that a first set output power is set when starting-upsaid generator; setting a target temperature of said exhaust gas as afirst set temperature; and changing said first set output power of saidgenerator to a current process output power when said exhaust gastemperature measured by said temperature sensor reaches said first settemperature.